Performance is generally increased with this technique because the physical hardware is not replicated so less system resources are used. However the negatives of this technique would be that the guest operating systems must be the same as the host sometimes even the same service pack.
The figure below shows a visual representation of OS virtualisation. At the very bottom of this diagram there is the network layer and the hardware layer found in all systems. Then there is the host operating system which communicates with hardware. Above this is where the virtualisation software sits and then there are the containers. Each container has its own system libraries that are separated from each other; underneath this is the virtualisation layer that communicates with the hardware. The virtualisation software that runs on top of the host OS is responsible for the management of each virtual machine and dealing with the requests to the hardware
Hardware emulation
Hardware emulation allows the physical hardware of a system to be replicated by the virtualisation software which will then allow guest operating systems to be implemented. Guest operating systems are installed in a virtual machine and the emulated environment is known as a virtual machine monitor (VMM). King (2003) states that a “virtual-machine monitor is a software layer that runs on a host platform and provides an abstraction of a complete system to higher level software”. According to Golden (2007, pp.24) “Hardware emulation is a powerful virtualization technology because it performs the guest OS modifications at runtime through a technique known as binary translation”. This therefore means that when the guest operating system is installed the requests need to be sent to the hypervisor instead of the physical hardware to achieve this the hypervisor has to modify the internal software of the guest operating system this is binary translation.
Wolf (2005) suggests that hardware emulation is mostly used “re-creating hardware that no longer exists, sharing expensive resources and porting software to different computer system architectures”.
The figure below shows how the physical hardware of a system would be replicated and utilised in hardware emulation. As the diagram shows there are 2 sets of virtual machines created and each of them have got a copy of the underlying hardware where an operating system can be installed and then various applications.
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Para-virtualisation
Golden (2007) states that Paravirtualisation is a type of server virtualisation, instead of emulating the entire hardware environment, there is a layer of virtualisation software that “coordinates” requests from the guest operating system to the physical hardware. With paravirtualisation multiple operating systems can run on the system hardware because the resources are being used more efficiently.
Shields (2007) states that paravirtualisation differs from other techniques because instead of replication hardware it uses a special “Application programming interface (API)” for each virtual machine. The guest operating systems must be purposefully coded to use the API.
Shared memory is a technique that is used by paravirtualisation to achieve better performance levels. This means is that the shared memory can be access by different programs. A paravirtualised system will use the shared memory to handle the traffic sent between the hypervisor and the guest operating systems, this is supported by Golden (2007).
The image below shows a paravirtualised system and how it operates
There are several similarities between the different types of virtualisation, in particular a hypervisor is used in both paravirtualisation and hardware emulation. Compared to OS virtualisation where the guests on the system are implemented above the host operating system so that each file structure can be copied , hardware and paravirtualisation need hypervisors to manage the different request that are made to the underlying hardware.
Hardware and paravirtualisation are also similar because the both require the guest operating system to be modified in the some way in order for the system to function properly. Whilst hardware emulation uses the term binary translation to do this paravirtualisation makes changes to the kernel prior to installing the operating system.
Hardware and para-virtualisation allow different operating systems to be virtualised whilst OS virtualisation only offers the virtualisation of the host. However with paravirtualisation the operating system needs to be open source so that it can be modified.
Paravirtualisation enables enhanced performance compared to other virtualisation techniques but considering the modifications necessary it would cause problems as certain vendors do not allow OS modification.
Virtualisation and cloud computing
Virtualization and Cloud computing
Cloud computing is based over the internet where shared resources are stored to give customers an on demand service.
Cloud computing is closely linked to virtualisation in the sense that it separates the software from the hardware Hurwitz (2009) et al. There are different types of virtualisation in the cloud as stated by Gillam (2010) these are storage, network and server virtualisation. A type of server virtualisation would be to map one physical resource to multiple partitions.
According to Gillam (2010) “virtualisation is extremely well suited to a dynamic cloud infrastructure because it provides important advantages in sharing, manageability and isolation”.
Many businesses will view cloud computing as a different way to use IT. This could lead to a change of original IT roles in the future so that the full power of computing can be utilised through cloud computing.
Conclusion
From this research report I have managed to gain an insight of the different virtualisation techniques that are available to use. Each of which have their own benefits and drawbacks for example although the performance of a paravirtualised system is better than a hardware emulation the choices of operating systems are limited because they need to be modified.
I have also have also seen how virtualisation and cloud computing are closely related and how important they are to each other.
Overall I believe that virtualization and cloud computing are essential IT because it allows businesses achieve greater capabilities and to easily increase capacity whilst not having to worry about buying new hardware or even new licences.
References
Sheilds, G (2007) The shortcut guide to selecting the right virtualization solution, realtimepubhlishers.com
Wolf, C., Halter, E (2005) Virtualization from the desktop to the enterprise, Vol.1, Springer-verlag New York
Hurwitz, J., Bloor, R., Kaufman, M., Halper, F (2009) Cloud computing for dummies, John Wiley & sons
Gillam, Lee (2010) Cloud computing: principles, systems and applications, 1st Ed, Springer
Golden, B (2007) Virtualisation for dummies, John Wiley & sons
Online Images
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